The conventional vehicle lights use tungsten light bulbs because tungsten light bulbs are easy to drive and maintain. The common vehicle lights include headlight, taillight, brake light, reversing light, and direction indicator. Conventionally, the vehicle light driving system categorizes the headlights using large amount of watts into a class, and the taillight, brake light, reversing light and direction indicator that use small amount of watts into another class. The taillight, brake light and reversing light are simpler in operation as they only need to turn on and off following the driver's instruction. However, the operation of direction indicator may be more complicated. According to ECE regulation 6 of EU, the direction indicator requires to meet certain blinking frequency, which is about 1.5 Hz, defined by taking the human visual and psychological reaction into account.
FIG. 1 shows a schematic view of a conventional driving system for tungsten vehicle lights. As shown in FIG. 1, a driving system 1 for tungsten vehicle lights includes a power control PWRC 10, a voltage regulator RGR 20 and an enabling switch ENSW 40 to drive tungsten taillight and brake light (L1) 31, reversing light (L2) 32, direction indicator (L3) 33. PWRC 10 outputs taillight and brake light enabling signal SC1, reversing light enabling signal SC2 and direction indicator enabling signal SC3 to RGR 20 and ENSW 40. RGR 20 outputs vehicle light switch signal SR to taillight and brake light 31, reversing light 32 simultaneously, and direction indicator 33 receives direction indicator enabling signal SC3.
Based on SC1, SC2 and SC3, ENSW 40 controls taillight and brake light loop signal SL1, brake light loop signal SL2 and direction indicator loop signal SL3, which in turns control the ON/OFF of taillight and brake light 31, reversing light 32 and direction indicator 33. For example, based on SC1, ENSW 40 grounds taillight and brake light loop signal SL1 to light taillight and brake light 31. In addition, PWRC 10 includes a flasher FLR 12 for outputting SC3 to enable ENSW40 to light direction indicator 33 with flashing frequency of 90 times per minute.
Because the driving mechanism of taillight and brake light 31, reversing light 32 and direction indicator 33 separates the loads, this mechanism can prevent taillight and brake light 31, reversing light 32 and direction indicator 33 from interfering with each one another. However, as the tungsten light bulbs consume more energy and are less durable, the LEDs gain much popularity and are widely used in many vehicle lighting applications, such as taillight, direction indicator, reading light, dashboard, and so on. These different types of applications require different voltage regulator structures, and yet with the same requirements for the vehicle LED driving circuitry of high translation efficiency, low current consumption, and LED current regulation. It is even more imperative to devise a simple and inexpensive architecture to realize the compound LED vehicle light driving system.
FIG. 2 shows a schematic view of a conventional LED vehicle light driving system. As shown in FIG. 2, voltage regulator RGR 20 provides vehicle light switch signal SR to LED taillight and brake light 51, LED reversing light 52 and LED direction indicator 53 simultaneously so that, based on SC3, ENSW 40 controls LED direction indicator 53 to flasher at the frequency of 90 times per minute; which will interfere with LED taillight and brake light 51, and LED reversing light 52.
The flashing of direction indicator depends on the flashing control relay (not shown), and the flashing control relay includes a flashing time control loop and a impedance determination loop. When the load of the lighting device is lower than a predefined level, such as lighting device short-circuit due to malfunction, the flashing time control loop will flasher at an abnormal frequency, for example, faster than the 90 times per minutes, to remind the user of the malfunction and trouble-shooting or repairmen is required.
Furthermore, the impedance determination loop for determining whether the load is normal is based on the energy consumption of the lighting device. Assume that a direction indicator consumes 20 W, and the front direction indicator and the rear direction indicator consumes 40 W in total. The design of the flashing control relay is to determine whether the load of the front and the rear direction indicators is over 20 W. If the load is over 20 W, the flashing is at the normal frequency. Otherwise, if the load is lower than 20 W, the flashing is at an abnormal frequency. However, as the LED consumes very little energy, the flashing control relay will treat LED lighting device as low load loop, and cause the direction indicator to flasher at an abnormal frequency.
Another problem of the conventional LED vehicle light driving system is that a shared voltage regulator is used by different lighting device load to reduce the cost. The driving system of the shared voltage regulator will cause the interference problem between circuits. That is, the brake light function may be interfered by the direction indicator to flasher abnormally, or the direction indicator may be interfered by the brake light to stop the normal flashing.
In the conventional technology, the LED lighting device interference problem may be solved by changing the LED energy consumption. However, while the above approach is fast, simple and low modification cost, the advantage of low energy consumption of LED lighting device is lost. Another approach is to modify the charge/discharge loop of the flashing control relay. The advantage of this approach is that the flashing speed can resume normal, but eh disadvantage is that the approach takes more time as well as more expertise for the modification. If all the direction indicators use LED, the abnormal flashing is still possible. Yet another approach is to install flashing control relay design specifically for LED. The advantage is that no further modification is required, but the disadvantages include high cost, expertise in replacing the vehicle control system relay, and normal flashing even when the LED lighting device malfunctions; in other words, the abnormal flashing is no longer available to remind the user for repair. Another approach is to change the driving circuit of the shared voltage regulator into an independent area circuit to provide lighting device with different loads individually. FIG. 3 shows a schematic view of the LED vehicle light driving system of an independent voltage regulation system. As shown in FIG. 3, the LED vehicle light driving system include two voltage regulators 20, 22 so that voltage regulator 20 provides LED taillight and brake light 51 and LED reversing light 52, while voltage regulator 22 provides LED direction indicator 53. The advantage is that the modification to lighting device design is easy, but the disadvantage is that the cost of driving circuit for independent voltage regulators will increase.
Therefore, it is imperative to devise an LED vehicle driving system with a single voltage regulator with a simple structure so that, without increasing the cost, the LED lighting device can be applied to the design of compound vehicle light and remains compatible to the general flasher that can avoid abnormal flashing when in low load and avoid interference between different loads. In this manner, the lighting efficiency can be improved and the cost and energy consumption can be saved.